Coexistence of ferromagnetism and superconductivity in Sn nanoparticles

We report on the observations of ferromagnetic spin polarized moment and superconductivity in Sn nanoparticles. Ferromagnetic spin polarization, which is characterized by the appearance of Langevin magnetic-field profiles for magnetization, persists even at room temperature. At temperatures below 15 K, magnetic hysteresis emerges in the weak applied magnetic-field regime. Enhanced superconductivity is found for particles with diameters smaller than 16 nm but larger than 9 nm. The presence of a magnetic field in the superconducting phase reveals a regime in which the magnetic susceptibility and magnetization increase with decreasing temperature. We attribute these behaviors to the coexistence of ferromagnetic spin polarized moment and superconductivity at low temperatures.